Deposition of metals, metal salts, metal oxides, and semiconductor materials on conformable substrates is well known. These coated films are used for example as electrical conductors, magnetic recording media, imaging films and decorative films. Coated films are also well known for flaking, cracking, crazing, and delamination. Mechanical handling of the films in manufacturing and in use frequently results in damage to the metal coating. Various techniques have been proposed to increase adhesion to substrate of metals and their salts and oxides, and of semiconductor materials.
Various mechanisms of surface adhesion of metal to substrate and of resins and polymers to metals are explored in "Adhesion Aspects of Polymeric Coatings" K. L. Mittal, ed. pp. 3-44, 107-113, and 265-280 (1984). Acid base interactions and surface topography are reviewed with the conclusion that the mechanisms of adhesion are not clearly understood. The authors examine the peel effect in polymeric coatings of strain caused by internal shrinkage. They observe that a coating will spontaneously detach from its substrate when the strain energy per unit area in the coating is equal to or greater than the interfacial work of adhesion. They examine the relationship between cohesive forces and interfacial strength to observe that an interfacial strength exceeding the cohesive strength will result in cracking and crazing rather than adhesive failure. Water stability of adhesion between polymers and metals is examined. Three surface characteristics are identified as relevant: physical and chemical reactivity or surface energy, morphology, and mechanical properties. The authors conclude that chemical bonds between polymers and metal surfaces alone cannot account for the water stability of adhesion. Surface treatments such as Chemoxal etching chromic sulfuric acid etching, sand blasting, phosphoric acid anodizing, chromic acid anodizing, ion bombardment etching and sulfuric acid anodizing are identified as methods to alter the micromorphology of surfaces and influence micromechanical mechanism of adhesion.
European patent application No. 81.301253.1 discloses decorative films and suggests vacuum deposition of discrete islands of metal particles on a smooth surface and thereafter coating the film with a protective top coat. These nonconductive films are said to withstand flexing and bending without microcracking because the metal exists as discrete particles on the film.
European Patent Appl. No. 81.305262.8 discloses polymeric surfaces which are pitted by penetrating the surface with a first reactant and thereafter with a second reactant. The second reaction reacts with the first reactant to produce pits in the film without substantially degrading the film between the pits. The first reactant is preferably an organic solvent that penetrates the film without swelling. The second reactant is preferably a chemical etchant that reacts preferentially with first reactant rather than the film.
U.S. Pat. No. 4,348,446 describes a polyester film which has been treated to be free of interfacial sticking during winding and to have excellent abrasion resistance. The film has microscopic protrusions on its surface and is prepared by adding inert particles in the coarse (1.5 to 2.5 microns), intermediate (0.5 to 1.5 microns), and very fine (less than 0.5 microns) diameter size ranges. The inert particles may be MgO, ZnO, MgO.sub.3, CaCO.sub.3, CaSO.sub.4, BaSO.sub.4, Al.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2 or the calcium or manganese salts, terephthalic acid, koalin, china clay, diatomaceous earth, alumina silicates, their hydrates, carbon black, or calcium phosphate. The inert particles are added to the polyester prior to polymerization, during polymerization, at the pelletizing stage, in the extruder after polymerization, or when the polyester is molten for extrusion. The film thus prepared is recommended for use as a base film for magnetic recording tape.
U.K. Patent Application No. 2,026,344 describes a polyester magnetic recording tape with micro roughness. Micro roughness is achieved by adding particles of calcium stearate, calcium acetate, or a calcium salt of a polyethylene terephthalate oligomer before or during condensation. Alternatively particles of inorganic substances such as kaolin and calcium carbonate may be incorporated into the polycondensation reaction mixture or into molten polyethylene terephthalate during film forming. The magnetic layer may be any of the conventional magnetic materials and a binder resin.
U.S. Pat. No. 4,247,496 discloses stretching a thermoplastic polymeric film and irradiating the film during or after stretching with UV light. The treatment is said to improve surface properties such as strip, oil impregnation, durability and deluster.
U.S. Pat. No. 4,123,277 describes various treatments to improve adhesion of a hydrophilic photographic emulsion to a hydrophobic resin such as polyester. Surface treatments such as chemical treatment, flame treatment, UV light treatment, high frequency treatment, glow discharge treatment, active plasma treatment, and ultraviolet laser treatment and the deficiencies of these treatments are mentioned. Use of an emulsion polymers as a primer without any surface treatment is also described. One such primer is a copolymer of butadiene, an ethylenically unsaturated monomer carboxylic acid and one other ethylenically unsaturated copolymerizable therewith. It is coated on a polyester film. The precursors for the copolymer disclosed in that patent are a monomer containing an N-alkanolamide moiety or an N-alkoxyalkylamide moiety, a component which provides a carboxy group, and a hydrophobic monomer. The monomers are polymerized with a latex polymerization process in aqueous solvents. An aqueous solution of the melted polymer is coated on the film with improved adhesion. The photo emulsion layer is selected from any of the conventional synthetic and natural hydrophobic high molecular weight compounds and suspended material such as silica halide, physical development nuclei such as silver sulfide or noble metal colloids or light sensitive materials such as diazo compounds.
The foregoing examples of coated films illustrate the complex and expensive processes for improving adhesion of coatings to polymers. These techniques require large capital expenditures for equipment and inspection control. A low cost, high quality, low waste coated film is needed for many applications. One particular application is electrically conductive films to be used as connectors or as conductors in electrodes.